Rear End Guide and Bolt Pattern Guide - Determining Differentials

Rear-Axle Spotter's Guide With Lug Patterns To Boot!

Photography by Christian Lee

Sport Truck, April 01, 2008

Not all of us are walking encyclopedias of automotive knowledge. We all know that one guy who can rattle off facts like how many '67 small-window C10s were made, but does that knowledge really matter? Well, it may not help build a truck, but it is cool to know. We wanted to give you some information that you might be able to use in the real world and hopefully help you build a better truck. With the assistance of some of our four-wheel-drive buddies, we compiled a guide to help you determine what rearend is under the truck and what lug pattern it has. This will just cover truck stuff, but that doesn't mean a car rearend can't be stuffed under your S-10. But that's a story for another day. We hope you find this guide useful, and until next month: Keep your eyes on the rearend.

TECH TIPAxle TerminologyTo prevent you from looking like a total newbie, here's some techno-jargon terms you should know when talking to the guy behind the parts counter:

Semifloating: The weight of the vehicle rides on the axleshaft, which also spins the wheel.

Full-floating: The weight of the vehicle rides on the axlehousing, and a ring of bolts in the center holds the axleshaft in place.

Integral: The ring gear and pinion gear are set up inside the differential housing.

Dropout: The carrier, or differential, can be removed as a single unit. It is also called the centersection.